Has something changed on the server? This used to work, but now it doesn't-- on multiple platforms.
This test was with a fresh install of 22.03.0-rc1 on a Ubiquiti UAP-Mesh (ath79).
root@OpenWrt:~# auc
auc (0.2.5-2)
Server: https://sysupgrade.openwrt.org
Running: 22.03.0-rc1 r19302-df622768da on ath79/generic (ubnt,unifiac-mesh)
No data available (61)